Hi Samantha,
Thanks for your patience can I please get you to try clearing the cache and cookies on your browser I have included steps to do this here, if however you have already cleared cache and cookies we would suggest trying an alternative browser to your preferred to see if you receive the same error or use a in private browsing window.
If the above does still not allow you to record your payment against your Invoice we will need to investigate this error further for you in order for us to do this we would require further details we are unable to receive any personal details such as e-mail addresses or company ID's so we would ask if you could either contact our product support team here or contact us on social media such as Facebook or Twitter messaging QuickBooks UK and we can arrange a call to you to raise the necessary details.
Please let us know if there is anything else we can help with in the meantime or if you have any follow up questions please let us know.
