Trying to filter all the contact under particular accountid. Need to have name filter also.
url:
https://alliedmodulartemp.api.crm.dynamics.com/api/data/v9.1/contacts?$filter=contains(first_name,'anhu')
Method:GET
Try below url should work.
https://alliedmodulartemp.api.crm.dynamics.com/api/data/v9.1/contacts?$filter=contains(firstname, 'anhu') and _parentcustomerid_value eq A6618972-2AFA-E911-A813-000D3A4AAC87