Getting module "Mail Merge Reports" working / malfunctioning template upload

Dear all:

Does anybody among the audience has a working installation of add-on module Mail Merge Reports?

We installed (paid) version 2.5.12 Premium on top of SuiteCRM 7.8.10. Even though we double-checked all installation steps we still can’t upload a locally created template file from local harddisk to server.
The module developer (Izertis) has not yet responded to any contact attempts for one week. :frowning:

I would love to get in contact with any successful users of said module.