Hey Samantha,
Have you checked if the suffix of the pair you are trying to trade is correct? I mean in Metatrader, you can see in the symbols side, there should be symbols like this EURUSD or EURUSD.i for example.
If you have placed the ones without suffix but there are also symbols with suffix, that could be the issue. In that case, you need to place the ones with suffix in the chart and try again.
Hope this helps!
If this did not solve the issue, please send me a screenshot so that I can assist you better!
Kind Regards,
Nikos