Seems to be called "Taxpayer's Identification Number" (short TIN), or "Numéro d'Identification du Contribuable" (short NIF) or "Nomero iranga umusoreshwa" according to https://businessprocedures.rdb.rw/procedure/13/47?l=en (specially https://businessprocedures.rdb.rw/media/TIN.jpg image linked in that URL).

• According to https://www.rra.gov.rw/fileadmin/user_upload/20180328_vsdc_technical_specifications_v.4.pdf it is 9 digits.
• https://world.salestaxhandbook.com/rw-rwanda

  Tax identification numbers can be verified with the Rwanda Revenue Authority, and will follow a certain format. The VAT number format is 000111111.

Search:

• https://etax.rra.gov.rw/nidAssignedTIN/

Examples:

• 102134442 from https://rab.gov.rw/fileadmin/user_upload/Publications/Template_Evaluation_of_Agricultural_templates-1.pdf
• 101365708 from https://www.judiciary.gov.rw/uploads/tx_publications/law_f72ce9098bc2b98030ed78319d60be6e1516714065.pdf
• 100384138 from https://www.minimex.co.rw/en/contact.php
• 101453690 from https://www.minijust.gov.rw/index.php?eID=dumpFile&t=f&f=55311&token=88e0d347d51f00f95cab0756e0598210e1950c92
• 101799622 from https://www.mininfra.gov.rw/index.php?eID=dumpFile&t=f&f=15962&token=ab2ccfebb30376c628e81ecdfac51d31615a2601
• 100054122 from https://rse.rw/IMG/pdf/i_m_rwanda_-_financial_statement_q3_2020-2.pdf
• 101909790 from https://www.umucyo.gov.rw/eb/common/fileIdDownload.do?fileId=092022122824746-7e63
• 101522783 from https://umwalimusacco.rw/wp-content/uploads/2021/08/EOI-TENDER.pdf
• 102259397 from https://thebridge.rw/wp-content/uploads/2021/07/Tender-Solicitation.pdf
• 102889110 from https://www.judiciary.gov.rw/uploads/tx_publications/law_8e7035e068f7046d16a509453862e0da1515136031.pdf
• 101982714 from https://bsc.rw/wp-content/uploads/2020/10/REOI-PUBLIC-RELATIONS-CONSULTANT.pdf
• 103752228 from https://www.bkinsurance.rw/reports_categories/2021/bkgi-annual-integrated-report-y2021
• 103449745 from https://naeb.gov.rw/fileadmin/user_upload/BELLA_FLOWERS_VACANT_POSITIONS.pdf
• 106278222 from https://www.regs.rw/ads/veterinary-doctor-rwanda-agribusiness-supporters-and-veterinary-consulting-services-ltd-rabsco-ltd-deadline-14-06-2018/
• 100003547 from https://www.brd.rw/wp-content/uploads/2022/10/TENDER_ADVERT_FOR_AFIRR_CAPACITY_BUILDING.pdf
• 102241010 from https://www.sonarwalife.co.rw/upload/ToRs%20to%20publish%20signed%20final.pdf
• 101806185 from https://rdb.rw/contracts/NEW_CENTURY_DEVELOPMENT_LTD-KIGALI_MARRIOTT_HOTEL.PDF
• 100003458 from https://bk.rw/files/newspaper/bk-group-condensed-fs-news-paper-q3-9m-2022
  • Also from https://bpmis.gov.rw/asset_data/form_201251/files/element_40_81e89d8ff79b4b6d2c77a2814ff80879-214-PROOF%20PAYMENT.pdf
• 102294535 from https://sonarwa.co.rw/IMG/pdf/sonarwa_g_i_accident_declaration_form-new_1_kinyarwanda_pdf_2_-2.pdf
  • Also from https://sonarwa.co.rw/IMG/pdf/announcement.pdf
• 102781991 from http://radiant.co.rw/wp-content/uploads/2021/03/DOWNLOAD-HERE-FINANCIAL-STATEMENTS-2020.pdf
• 102750860 from https://www.impact.rw/synology.html
• 100003547 from https://www.brd.rw/wp-content/uploads/2022/10/CDAT_Project_Accountant.pdf
• 100005973 from https://www.cogebanque.co.rw/wp-content/uploads/2020/03/Financial-Statement-Q3_2017-Final.pdf
• 110842971 from https://rwandabar.org.rw/attached_pdf/ITANGAZO%20RYA%20CYAMUNARA%20Y'IBIKORESHO%20BYAHOZE%20ARI%20IBYA%20SPORT%20VIEW%20HOTEL%20LTD-1619618266.pdf
• 102175071 from https://www.judiciary.gov.rw/uploads/tx_publications/law_065982e894fcde21153454b2ea4b2a8a1451462037.pdf
• 108311419 from https://www.excellaproduce.rw/?rubrique3
• 107610471 from https://rse.rw/IMG/pdf/appointment_of_a_chief_credit_officer-2.pdf
• 111414698 from https://www.kanis.rw/shop/ETS-MAGASIN-KAJAL-LTD-/all_products?page=2
• 107215286 from https://www.ombudsman.gov.rw/index.php?eID=dumpFile&t=f&f=11201&token=6f1a01a9c99aa1b64919790ad6d4e8e826c7543c
• 100475843 from https://rcb.rw/IMG/pdf/tender_interpretation_services.pdf
• 104940576 from http://www.tender.rw/advertisement-for-service-of-asset-inventory-and-codifications
  • Also from https://vuba.co.rw/job-in-rwanda-view/11
• 102050982 from https://www.ultimatelogistics.rw/ultimate-logistics-about
• 101302769 from https://www.intertech.rw/about-us/
• 104741833 from https://umuryango.rw/index.php?page=print&id_article=59639
• 108708667 from http://www.bps.co.rw/contact-us/addresses
• 10 7826151 from https://universe.rw/about%20us.php
• 103745842 from https://www.kesiinvestments.rw/
• https://acgdr.rw/regmember/

  107907110
  102517684
  108630474
  102517692
  107877617
  100842224
  111304003
  102312520
  101411623
  102966085
  102026860
  120201204
  106363818
  102925497
  102503783
  101651018
  102874107
  106208031
  107993781
  101611834

• 228 numbers in https://umucyo.gov.rw/um/upe/mng/procuringEntitySearchPopup.do;jsessionid=220BD881DE7D1639CC5BA35310421388.ec2

  101313744
  101338997
  101832055
  101898817
  101742978
  101402045
  101369930
  101605491
  100600260
  101658248
  119491475
  100805888
  101725879
  101674807
  102420381
  101056837
  102580229
  103548327
  101669410
  100600293
  102760872
  120335672
  101332193
  101717108
  103372620
  111598890
  113333440
  102043412
  101351105
  101529751
  101337363
  001337363
  113653574
  101406098
  101639016
  101639016
  101932000
  101398024
  103012202
  100834445
  101992637
  111704557
  101846992
  101828601
  101734460
  120385529
  101790784
  101735377
  103144513
  102872114
  101566434
  102279886
  116904634
  101888471
  101587056
  101808480
  100834501
  101931624
  101615259
  101628996
  101868137
  101403075
  101823693
  111444309
  120434728
  101494914
  101507188
  101515599
  101599094
  101743183
  101354055
  001354055
  101330738
  100842023
  102831150
  102000244
  102106636
  101419173
  102065987
  100604778
  102502361
  101378645
  101667834
  100600431
  103058257
  101853419
  101052213
  101662117
  101474514
  102190813
  101896784
  119776770
  102496275
  100834479
  101397575
  101397028
  107433062
  100600456
  107429609
  107433046
  120576276
  107429659
  100840910
  101852144
  101541027
  101673002
  101687703
  101746067
  103644998
  101488481
  119491475
  100805888
  101725879
  101674807
  102420381
  101056837
  102580229
  103548327
  101669410
  100600293
  102543856
  107794257
  100600423
  103047835
  101671026
  101553163
  103061847
  106891578
  102704958
  101792173
  101774925
  101408122
  101535199
  101315485
  101880603
  101711471
  101753309
  101822442
  102059291
  120263565
  102058377
  102058506
  102060367
  101785453
  101895086
  101909790
  100604752
  000604752
  111983517
  112946918
  101310933
  111954363
  1134937870
  113493787
  100600407
  100604703
  100021341
  222222222
  107426422
  101435463
  100600415
  102842061
  101611484
  101465702
  101465050
  101708622
  113691687
  100834095
  111409897
  100604818
  101914738
  102669821
  101463866
  101336481
  102040317
  101515092
  101407950
  101680288
  101665156
  119674677
  102568316
  100100749
  100202958
  106809180
  101764065
  116906081
  102460748
  101394054
  108531302
  107861625
  102643158
  107111882
  107929979
  101868186
  101787496
  106890612
  101704629
  101449322
  107812839
  100600448
  100600570
  102495653
  100600375
  106891723
  102107429
  101635502
  100841280
  102760880
  102432672
  101766817
  102420194
  113171196
  103683101
  111194286
  102269008
  103527135
  112358054
  113346076
  102043283
  111193827
  101457807
  101366974
  101327114
  101382424
  103124074
  103086634
  103260393
  100600359
  101895712
  101864567
  108650016
  113423733
  103369480
  100600391
  101808987
  101647214
  103370539

• Hundreds of them in
  LICENSED-CFA-SEPT.-2017-4 pdf.pdf attached just in case (originally retrieved from https://rwandatrade.rw/media/LICENSED-CFA-SEPT.-2017-4%20pdf.pdf )
• https://www.google.com/search?q=site%3A.rw+%22TIN%22