The Rekado app has options to update payloads to the latest, or even add your own, but the latest should work anyway.
Next thing I would check is the cable. To inject the payload, the phone needs to act as the USB host, and with USB C-to-C cables, it's unclear which side will be the host. This is why the Rekado instructions advise to use a USB A-to-C cable with a USB OTG adapter. The OTG adapter will always be the host side. Llike this, sort of:
[Phone] <male USB C, or microUSB if the phone is that old ---- USB OTG adapter ---- female USB A> <male USB A ---- cable ---- male USB C> [Switch]
USB 2.0 cables and adapters are more than enough for this, no need for USB 3.x.
The Trinket M0 is also one of SAMD21-based boards I mentioned before, that can be used for the V1 mod. I haven't used one yet, though.