According to the SAP tutorial guide, you are using URL https://tools.hana.ondemand.com/oxygen to install ABAP Development Tool in the Eclipse. In Eclipse, https://tools.hana.ondemand.com/oxygen could not be found as below:
SAP Development Tools for Eclipse
Could not find https://tools.hana.ondemand.com/oxygen, unable to read repository at, Install New Software, certificate path, unable to find valid certification path to requested target , KBA , BC-DWB-AIE , Installation and infrastructure for ABAP tools in Eclipse , Problem
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