If it's one of the older OSTC4 (smaller serial 180 or so) then you still have the Qi 1.1 standard. With this, the positioning is a bit tricky. but we'll modify your unit free of charge into the new 1.2 standard (10mm transfer range compared to 4mm) and replace your charger with one of the new models. Please contact us then: firstname.lastname@example.org
For both versions, a USB power supply with 2A is recommended and 1A is minimum.