Patti LaBelle -- Invites Pie Guy to Thanksgiving ... With Strings Attached

Patti Labelle showed her gratitude to the guy who helped make her sweet potato pies a sensation ... but apparently the invitation came with a condition.

The video is hilarious ... Patti and James are together at Patti's home in Philly, and they're singing up a storm. But notice they're both holding one of her sweet potato pies ... the ones that flew off the shelves at Walmart after James sang its delicious praises.

Patti took some heat after telling our photog her pie success was all her doing, not James'.