I am using file_var_write and file_var_read to save, then load data from a .txt file. You will also need file_open_write, file_open_append and file_open_read to get these things working.

It is complex and tricky to set up, but I was unable to get around the problems caused by Game_save and Game_load ... well worth the trouble.

See my games here: https://www.indiedb.com/company/michael-klaus-schmidt