Wont work for me

Im extremely disappointed, especially after reading such positive reviews of this app because it doesnt work for me at all! When I log in I get a message "code 403 error message: you are not a sandbox user of this client"???? If the developers or anyone have any suggestions regarding this please advise but again, just a disappointment. I guess I will try another similar app.

Kat4760 about Insta Reposter - Regram and Reshare Video & Photos, v1.1