Getting error when try to save shipping information for user using magento 2 api

Unable to save address. Please check input data.

It's a strange error we have it sometime, to solve it in some cases you execute this query 

SELECT entity_id, customer_id FROM quote WHERE customer_id != 0 AND customer_is_guest = 1;

and then update the records by this query 

UPDATE quote SET customer_is_guest = 0 WHERE customer_id != 0 AND customer_is_guest = 1;

reference url :

https://stackoverflow.com/a/58086757/4135373