Spack: Multiple Packages (WarpX install)

Hi, i am trying to install openPMD on my ubuntu20.4, X64. I need it to visualize WarpX codes. I don't know why it is not possible to compile warpX with

```
make -j 4 USE_OPENPMD=TRUE
```
as described here: https://warpx.readthedocs.io/en/19.10/building/openpmd.html

So, I tried:
```
spack install openpmd-api
spack load openpmd-api
```
But I got this error:

```
Error: openpmd-api matches multiple packages.
Matching packages:
aulbntd openpmd-api@0.14.4%gcc@9.4.0 arch=linux-ubuntu20.04-ivybridge
zx572t3 openpmd-api@0.14.4%gcc@9.4.0 arch=linux-ubuntu20.04-ivybridge
```
Thanks for your help.