When adding a video to your page you must enter the Video ID in order for the video to play as expected.
To find the video ID you would firstly locate the video you wish to use on Youtube, below this video you will find and select the Share button.
Once you have selected this, Youtube will give you options to share the video, from here you can copy the last part of the link provided as shown in the image below:
Note: The part of the link highlight in the image above is the Video ID, you will then input when adding your video to your fundraising page on iDonate.
If unsure where to add this on iDonate, please see :- https://idonate.zendesk.com/hc/en-us/articles/360020878619-How-can-I-add-images-video-s-to-my-fundraising-page-