firmware upgrade failed incorrect file getting error in my router tplink 6400

@Kevin SG my version is v5 i have a 4g router model mr6400 Kevin SG wrote Hi, Is the Internal Port 8080? What's the working mode and WAN IP of the MR6400? dynamic dns and dmz 4g router port...

@Kevin_Z Error code: 71211 Failed to upload upgrade file. Please select the correct file.

Error code: 71211 Failed to upload upgrade file. Please select the correct file.

@Kevin_Z Error code: 71211 Failed to upload upgrade file. Please select the correct file.

i have tplink mr6400 v5 i cannot upgrade v4 because i have new version V5 on my tplink mr6400 plz help me i want to switch back v4 the router will be show upgrade incorrect file i cannot upgrade old...