Update your post to include full system hardware specs and OS information.
Go online to find the applicable User Guide/Manual for the motherboard. Pay careful attention to make, model, and version.
Be certain that you are at the manufacturer's website. Just because ther manufacturer's name is in the URL that does not always mean that you are really at the manufacturer's website. If warnings appear then leave the website immediately.
The User Guide/Manual will provide some listing of supported RAM and RAM configurations.
There will most likely be some instruction to visit the motherboard's manufacturer's website to obtain more up to date information via the QVL (Qualified Vendors List).
Also - review the entire User Guide/Manual to double check all connections and configurations.
Some motherboards, for example, require that the first physically installed RAM be placed in a specifc slot.
Error codes may or may not be helpful: error code 0xc0000221 being very generic.
Do an online search for the error code and read more about it. However, do avoid downloading any apps, utilities, or such stuff claiming to "fix" the problem. Many of those products are likely to show up no matter what error code is in question.