here is an older post from me that explains how you can use the “Make an API Call” Modules in Make to be able to search for specific entries. In that case, it was an invoice but the same can be done for clients.
GET /api/v1/clients?page=1&per_page=50&name=Test will search for all clients that have “Test” in their name. I guess you can also search for an email address. Although email addresses belong to contacts and not clients. I haven’t tried this but maybe @hillel can point you in the rigth direction. Something like &contacts.email=xxxxxxxxx ?
Another option could be to created a data store in Make that has the client id from Invoice Ninja and the emailadress from Woo Commerce. So it creates a matching table.
Add a record: https://www.make.com/en/help/tools/data-store#add-replace-a-record
Search a record: https://www.make.com/en/help/tools/data-store#search-records-935244
And of course Hillels option to store the client id in Woo Commerce does work too as long as you get that client id back from Woo Commerce.
Happy New Year
Gijs