Fixed IP address
Seravo WordPress upkeep solution is a cloud service in which the clients sites are located in server clusters formed by many physical machines. This kind of architecture boosts the speed of the WordPress sites as well as adds redundancy and the ability to withstand load. This also means that it's not possible to get a fixed IP in Seravo upkeep by default.
In theory the only way to get a fixed Ip for your website is to buy a complete server or a cluster of servers from Seravo separately. This kind of a solution is, however, very expensive and the cost is most likely reasonable only for the largest of sites.
IP addresses as a method of authentication
If the IP address is required for authentication in some API etc. you can choose to add the IP addresses of the server cluster to that service. You must, however, take into account that all the other sites in that cluster are using the same IP addresses and make a decision if that's a risk you're willing to take. You can get the IP addresses of your sites cluster by asking for them from our customer support.
Generally speaking IP address is a bad and insufficient way of authentication. If the WordPress site is using some external API that requires authentication, you should then use an API key that's transferred with the HTTP request or something similar cloud based modern technology solution.
Routing the traffic via another server
One alternative technique is to route the API traffic via another server. You can get more information on how to implement this from our customer support. This way the external visitor to the site will always see the same IP address for the site even though the WordPress site itself is still in the same clustered environment to improve its redundancy. The same server can also be utilized if the external API service requires some exotic communication protocol or something alse that can't be done in the WordPress environment.