docs: Update admin-api.md (#10056)

* Update admin-api.md

Added note on ID syntax

* docs: Update admin-api.md

* Update admin-api.md

Periods can be added as special characters too

docs/en/latest/admin-api.md

@@ -277,6 +277,10 @@ curl 'http://127.0.0.1:9180/apisix/admin/routes?name=test&uri=foo&label=' \
 
 Route resource request address: /apisix/admin/routes/{id}?ttl=0
 
+### Quick Note on ID Syntax
+
+ID's as a text string must be of a length between 1 and 64 characters and they should only contain uppercase, lowercase, numbers and no special characters apart from dashes ( - ), periods ( . ) and underscores ( _ ). For integer values they simply must have a minimum character count of 1.
+
 ### Request Methods
 
 | Method | Request URI                      | Request Body | Description                                                                                                                   |
@@ -871,6 +875,8 @@ An Upstream configuration can be directly bound to a Route or a Service, but the
 
 Upstream resource request address: /apisix/admin/upstreams/{id}
 
+For notes on ID syntax please refer to: [ID Syntax](#quick-note-on-id-syntax)
+
 ### Request Methods
 
 | Method | Request URI                         | Request Body | Description                                                                                                                      |
@@ -1180,6 +1186,8 @@ Currently, the response is returned from etcd.
 
 SSL resource request address: /apisix/admin/ssls/{id}
 
+For notes on ID syntax please refer to: [ID Syntax](#quick-note-on-id-syntax)
+
 ### Request Methods
 
 | Method | Request URI            | Request Body | Description                                     |