Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/STMicroelectronics/STM32F7x8/OTG_FS_DEVICE/OTG_FS_DIEPTSIZ0#0x0
device endpoint-0 transfer size register
Transfer size
Packet count
https://github.com/cmsis-svd/cmsis-svd-data