How to retrieve the customerIdentifier from Splynx

We have a flutter application using the Splynx system. Is there a way we can query the customerIdentifier by giving the customer email and password combo?

It seems that the registerCustomer api call is the only call that returns the customerIdentifier.

All other api calls require the customerIdentifier to send a request.

Any feedback will be appreciated,
Thank you.

i have making a flutter app for a customer so today i figure out how to retrieve by search if can help you.
i am using the postman for tests so the url is like this bellow.[email][]==&main_attributes[email][]