If application sends the claims with data in the form of extension attribute registered on a different application, a claims mapping policy must be used to map the extension attribute to the claim.
New-AzureADPolicy -Definition @('{
"ClaimsMappingPolicy":
{"Version":1,
"IncludeBasicClaimSet":"true",
"ClaimsSchema": [
{
"Source":"user",
"ID":"employeeid",
"SamlClaimType":"http://schemas.xmlsoap.org/ws/2005/05/identity/claims/employeeid","JwtClaimType":"employeeid"
},
{
"Source":"company",
"ID":"tenantcountry",
"SamlClaimType":"http://schemas.xmlsoap.org/ws/2005/05/identity/claims/country",
"JwtClaimType":"country"}]}}')
-DisplayName "ExtraClaimsExample"
-Type "ClaimsMappingPolicy"

accesstokenAcceptedVersion
must be set to supported value 1, 2, or null , depends on the issuer enpoint obtained from the token.
- "
acceptMappedClaims
" must be set to true, for single tenant app.
Also do make sure to give claims under accessToken in manifest .

Note:
- If want to have the claims in the access token then you may need to modify the manifest of the resource app. i.e.; If you have an web App
that calls Web API B and you want the claims in the access_token then
you need to modify the manifest of web api B.
- Only extension attributes on user objects can be used for emitting claims to applications.
When adding claims to the access token, the
claims emitted are for a web API and not requested by the
application. So you will be able to see only claims emitted are for
access tokens requested for the application webApi.
Reference: Use Azure AD directory extension attributes in claims - Microsoft Entra | Microsoft Learn