If you're using Retry's Custom Midway Object feature (!use_custom_midway_bar = 1 in the settings) and you want to insert other custom objects with ObjecTool, you may need to do some preparation steps depending on which ObjecTool you're using (see info below).
One thing to keep in mind in any case is that Retry will use slots 00-1F, 40-41 and 50-51 of the Custom Normal Objects (i.e., objects with id 2D) for its custom midway bars, meaning that you can't use them in ObjecTool. You're free to use Custom Normal Objects 20-3F, 42-4F and 52-FF, as well as all Custom Extended Objects available.
If you're using Arinsu's ObjecTool, you don't need to do anything else, it should just work out of the box. Just make sure you inserting Retry after having inserted ObjecTool at least once. If Retry's custom midways don't spawn, reinsert ObjecTool again.
If you're using imamelia's ObjecTool, you need to modify its asm file a bit to make it work properly with Retry.
Open objectool.asm and remove these lines (they're towards the top of the file):
org $0DA415|!bank ; x6A615 (hijack normal object loading routine) autoclean JML NewNormObjects ; E2 30 AD 31 19 NOP ;
After doing this, just patch objectool.asm.
If you want to remove Retry's Custom Midway Object feature while keeping ObjecTool, you'll need to place back the code that you removed in objectool.asm (and make sure you run Retry with !use_custom_midway_bar = 0).