Soles that are too stiff can cause it. People are different, so there could be different causes and remedies. Getting rid of it can be as painful as the band aids that help with the pain but not a cure. My story:
Run and jump athlete all of my life. Baseball, basketball court sports, etc. Got it really bad in my late 30s. I would slide down the stairs in the morning on my behind after a night of hooping it up. Gave up all court sports including my beloved basketball in my early 40s. I turned to cycling. Wife was/is a runner and wanted me to become one. Did lots of reading. Came to the conclusion that my feet had gotten weak and stiff from all those years wearing heavily structured/support court shoes. I threw away of all my shoes and got ones with cushioning, but no support of any kind. Bought some transition running shoes for people that were moving to barefoot running. The first run, all I could manage was about a mile before my feet were hurting so bad I could barely walk back. Woke up the next morning with no plantar pain. Went out the next day and managed to run a little farther before limping back to the house. Next morning, no plantar pain. Went through a month of that before the pain on the runs disappeared all together. That was around 15 years ago. Since then, the plantar is gone. I have some scar tissue I can feel, but no pain. Still roll it with a golf ball and stretch. I've ran around 10K miles since then including 14 marathons and various tris/obstacle races in addition to the cycling.
If you have access to a pool, swim or practice your leg kicking on the side or with a paddle board. That will stretch that area and the connecting tissue better than most of the other exercises combined. Good luck.