I would like to connect 3 solar panels to my new AC 300-B300

I recently purchased the AC300, B300 combination. I am attempting to connect 3 Harbor Freight 100w solar panel. Not stated on the box or in the instruction included but only stated on the back of the panel is a statement that the panels should not be connected in series. I made inquiry with Harbor Freight as to why not in series. They responded promptly that connecting in series would damage the diodes in the box. I presume they are referring to the bypass diodes.

Given that the panels are each rated at 5.56 amps and max 24v, I could do a work around by connecting 2 panels in parallel on one feed and the third on the other, but I would prefer to reserve that 2nd feed for future panels.

Brand new to solar so please excuse my faulty terminology. Is there a safe way to connect all three panels into one line in?

I don’t think anything should come of harm in a series configuration. Bypass diodes are to minimize the loss when a part of a panel is shaded. Should not matter in this case. A 3 series (3S) config would be your best option here.