Your message is read and answered by a person, not a ticket system, usually within one business day.
Write to extracarts-beta@q4rl.com (the e-mail link is in the footer).
Found a vulnerability, or need to report a data incident? Write to security.extracarts@q4rl.com — this mailbox exists solely for this purpose; reports are handled with priority. For data incidents the DPA additionally applies: as your processor we notify affected merchants without undue delay. Machine-readable: security.txt.
Many questions are already answered in the FAQ — pricing, compliance, sending frequency, and data handling.