This should convince your manager

 The following email is a simple template you can modify to your specific needs. It is short and up to the point.
NOTE: There are 7 areas in <> that you'll want to customise.  

SUBJECT LINE: Suggestion to sponsor OR purchase premium VIP pass for <delete accordingly>  the 1st Virtual Horizon Europe Summit

Hi <Insert your Manager's name here>,
As you know, keeping up on the the Horizon Europe tactics and promoting our Horizon Europe services or the funded projects we are involved is essential for our organisation's success.  <You may want to customise this first sentence based on your unique needs>
The organiser of the 1st Horizon Europe summit has invited and is currently interviewing top experts in Horizon Europe and the interviews will be broadcasted during the summit week from Monday  31 May till Friday 2nd Oct till Friday 4 June 2021. 
​The host is Mr. Nikolaos Floratos and Funding Expert Academy, ranked no. 1 as "funding expert" in google search results and have access to a very big community of Horizon Europe actors through their social media, affiliates and email subscribers community.
The participation to the event during the live broadcasting week (31 May -4 Jun 2021) is free and any individual that wishes to have life-time access to the training sessions as well as to the training material can purchase a premium pass that is currently under great discount (only €97) and allows anytime access to all training and interview sessions.

​I believe that supporting this event as sponsors will give us a wide exposure to the Horizon Europe community. We can sponsor as an organisation or as "an Horizon 2020 funded project" we are already involved so in that case the sponsorship fee to be considered as eligible cost for communication and dissemination activities under "other costs" category in our project. <You may want to customise this sentence based on your unique possibilities>

The sponsorship packages range from €250 to €1500 and all of them include from 1-10 complimentary Premium/VIP passes.  There is a quick overview on the sponsorship packages here: https://www.horizoneuropesummit.eu/sponsorships.html​ <You may wish to delete this paragraph in case you are not interested in sponsorship packages but in just purchasing one or more VIP premium passes for some members of your team>
With your permission, I'd like to secure a sponsorship package OR the purchase of one or more Premium/VIP passes for some members of our team. <You may want to customise this sentence based on your unique possibilities and needs>

Thanks for considering it and I am looking forward to your response.
<Insert Your Name Here>