Hello Maria,
In SMW01, can you highlight the BUPA_MAIN row(as displayed in your screenshot) and check for receivers(there's an icon that you can click), and also the errors(if any).
I think there'd be no receivers displayed.
Then check trnsaction SMW3_00 and ensure BUPA_MAIN isn't listed in that.
Then you can check the SMQS and SM59 settings for the ECC destination. While you're at it, also
ensure that the R/3 destination is maintained as a site in transaction SMOEAC.
If all settings are in place, then we can be sure that data exchange between ecc and crm is not a problem.
So we can then focus to the PIDE settings in ECC and SPRO settings in CRM and ensure that the BP settings(e.g. number ranges etc) are fine.
Regards,
Rohit