Hey,

Most likely your performance in the interviews was a bit lower, and so while they like you, they didnt see you fit at the level.

But this could be speculation..maybe they are tight on budget or something else changed in the backend or they interviewed you for the wrong level from the start and no one explicitly said anything. Happens!

Here's my tips:

• Best understand the details with HR first to see whether feedback is around your level of performance in interviews
• If it indeed is, approach this with win-win in mind. No blame game. Tell them how keen you are make this work and ask for if they are willing to discuss this further
• Be ready with your options- are you convinced you are ready for the next level and have the skills to be succesfull?! Whats the impact on your compensation?! If you have interviewed elsewhere and performed well at the next level, then use this as a negotiating point
• if its an admin error or some other issue, am sure HR themselves will collaborate with you to find a way

Otherwise, take/reject the offer depending how badly you want this and/or have other options brewing.

All the best.