Problem with memory upgrade

Hello there, hope everything goes well, we have a problem with a memory upgrade procedure, when we try to add the new 1 memory (64GB) the system gave us a message like:

- mixed DIMM detected dell fatal error ( I try to put it into the slot A5 and A6 white ones)

Also, it shows us another error when we put the memory in another slot (green or black ones)

The DIMM module on memory slot A12 is populated out of order in the DIMM channel. (I try to put it into the slot A9 and others)

Hardware used:

- Server Dell R730 already with 32GB RAM - Dell Memory

- 64GB - 4Rx4 DDR4 LRDIMM 2400MHz

I have a theory and It can be because the server has RDIMM already integrated (32GB), it won't let us add another type of memory like LRDIMM, What do you guys think? and What can we do to solve this issue?

thanks in advance for your help, I will appreciate any advice, be safe! Iván M.