my Ipad won't download the newest update IPADOS 15.3.1 i tried deleting it and redownloading it and it still won't update, it gives me an error

These support pages outline both the available methods by which the update can be performed - and troubleshooting should you experience difficulties:

Update your iPhone, iPad or iPod touch – Apple Support

If you can't update or restore your iPhone, iPad or iPod touch – Apple Support

If your iPhone, iPad or iPod touch won’t update - Apple Support

iOS update and restore errors – Apple Support

Be aware that your iPad may be too far behind the current version to be updated directly from iPad settings. As such, you will likely need to use a computer to perform the update. You will need access to either a PC (with iTunes installed) or a Mac (with iTunes or Finder - as appropriate for the installed version of MacOS). Ensure that your installed version of iTunes has been updated to the most recent version; the essential device drivers are included.

Download and use iTunes for Windows – Apple Support

Update to the latest version of iTunes – Apple Support

Update software on iPhone, iPad or iPod touch in iTunes on PC - Apple Support

If you have a beta profile installed, ensure this has been removed from your iPad - as, otherwise, installation of production software updates may be inhibited. This support page provides the necessary information to remove the beta from your iPad:

How to uninstall iOS beta software - Apple Support

You should note that for your iPad to install an available update, its battery must be charged to at least 50% capacity - and/or be connected to its Power Adapter. Similarly, the iPad can only be updated over a standard WiFi connection - or be updated by a PC or Mac using iTunes or Finder - over a USB connection.

same problem, my daughter's ipad, one of the 6th generation, restarted and the apple began to appear on a white background over and over again

I put it in DFU and when I connected it I could neither UPDATE nor RESTORE, it gives me an error, I already tried changing, cable, on another mac, etc.

what do I do????

I already tried several cables, on two different macbook pros, but it still gives 4013

maybe wait for Tuesday in case version 15.4 comes out?

I see that version 15.3 gave me all these problems..

if it were to be something hardware? What I can do ?

As you probably know by now, iPadOS 15.4 was not released. You can wait for that, but if you need the device, you are going to have to do something quicker. It will probably be at least a week or so before 15.4 is released, given the information about new products provided in the event.

Well, 15.4 came out, I'm going to try to fix the ipad, all this is already a headache...

If it is not solved, I do not know what else to do, take it so that they take it as part of payment in a new purchase?

If it is not solved, see about having the device examined by Apple. If you have an Apple Store close by, make a Genius Bar appointment. If not, then use the Get Support link at the top of the page here to contact Apple Support.

See the instructions here, If you see error 9, 4005, 4013, or 4014 when you restore your iPhone, iPad, or iPod touch - Apple Support

Your iPad “iPad” could not be restored. An unknown error (4013) occurred.

Contact Apple Support, or if you have an Apple Store close by, make a Genius Bar appointment to have it checked there.

Do you think it's a good idea to wait for today's event and if iPad 15.4 comes out, try updating it to that version?