@kindandbrave: Thanks for this question. I am also struggling with this on a website I'm currently building pro bono for an author and related non profit that he's launching.
After many rounds with Squarespace Support it does appear that at this time, it's not possible to customize any copy on the donation confirmation page.
Our key challenge with this is that this page currently pulls the Site title, instead of the Donation Title, into the confirmation description, and the Site Title on this site is the author's name –– very different than the actual recipient of the funds, which is actually an organization soon to get 501 (C)3 funding.
Because it is possible to customize every other notification in the Order/Donation Confirmation communications stream with the name of the actual recipient of the donation -the Donation Title, as opposed to the Site Title (which Squarespace has chosen to program into this final step of the order communication stream within the website itself but then not let you edit), this creates significant discrepancy and confusion for donors as to who/what they are donating to. As someone who has worked in marketing and fundraising for non-profits for a decade, I will offer that this is a serious problem. In this instance, particularly, it's also awkward and uncomfortable, as for a transitory moment the donor may think they are actually donating to an individual instead of the organization, despite the fact that in every other confirmation throughout their process, and in our customized Donor email confirmation- they are reassured that they are contributing to the organization itself.
After many (many) rounds with Squarespace Support on this issue over the past week, I Googled it externally and found an incredible and thoughtful resource in a Squarespace Consulting group in Ireland called SFDigital . They are vetted through Squarespace and the key partner, Paul, @paul2009 works with Squarespace's through their "Hire an Expert" programme. He was incredibly helpful, savvy to the challenge and kind enough to actually spend some time offering a few free thoughts on the matter via Chat. SFDigital's thought –– if I am paraphrasing correctly, as I am a photojournalist, designer and fundraiser and not a developer –– is this is perhaps a bug in Squarespace's programming in that they are correctly using the designated Donation Title on all other donation page communications and the email confirmation, but defaulting inappropriately to the Site Title, for some reason, on the Thank You page.
Site URL: https://rogerpbriggs.org/
Attachments: For clarification of the explanation above and to visually show the donor's confusing experience, I've attached a series of screenshots of the checkout and confirmation process of a donor making a contribution to this site. They clearly show the Donation Title in all places until the final Thank You confirmation, and are attached in the order that a donor will see them.
The final screenshot is a capture of the back end of the Donation Confirmation EMAIL that donors receive in their own inbox after they may a donation- as opposed to the immediate uneditable pop up "THANK YOU" message/Donation Confirmation PAGE they see on the site (as shown in the fourth screenshot attachment.) This back end view seems to clearly show that there is a tag for a Donation Title, as opposed to a Site Title, that is being used in other elements of the Order Confirmation process.
Thanks to all who have additional thoughts to contribute on how to resolve this issue!