I am using a Boss FV-500HI pedal. Technically, it’s a volume pedal but it is also an expression pedal. The biggest problem I see people having is not with the expression pedal, but rather the cable – make sure you are using a TRS cable, not TS. If you’re not sure, just buy a new TRS cable. You can get a decent Hosa TRS cable for $7 or so. I have this one:

https://www.amazon.com/gp/product/B0011X95CY/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Now as for the issue with the sweep, I actually got a really good answer in a Facebook group.

“With the box in bypass mode, and the expression pedal set to heel down, hold the middle button down until the green LED appears by the FX section. Adjust settings for heel down, then move to toe down and do the same. Don’t toggle between heel down/toe down swtting while programming. When satisfied, press and hold middle button until the green LED turns to red, done. “

I did that and it works great…and it actually is in the manual, but I didn’t read the manual that carefully.